1. Field of the Present Invention
The present invention relates generally to cabinets for rack-mount computer and data storage equipment, and, in particular, to thermal management of cabinets for rack-mount computer and data storage equipment.
2. Background
Racks, frames and cabinets for mounting and storing computer and other electronic components or equipment have been well known for many years. Racks and frames are typically simple rectangular frameworks on which electronic components may be mounted, or on which other mounting members, such as shelves or brackets, may be mounted which in turn may support the electronic components. Cabinets are typically frames on which panels or doors, or both, are hung to provide aesthetic improvement, to protect the components from external influences, to provide security for the components stored inside, or for other reasons.
Racks, frames and cabinets have been built in many different sizes and with many different proportions in order to best accommodate the components which they are designed to store. Components stored in these enclosures may include audio and video equipment and the like, but quite frequently include computer equipment and related peripheral devices. These components typically include housings enclosing internal operative elements.
As is also well known, the electronic equipment mounted therein tends to generate large amounts of thermal energy that needs to be exhausted away from the equipment effectively in order to maintain the equipment in proper operating order or to prevent damage thereto. The problem can be especially significant when the components are enclosed in cabinets, because thermal energy generated thereby can concentrate within the equipment enclosure and cause the components to overheat and shut down. As equipment becomes more densely packed with electronics, the quantities of thermal energy have continued to increase in recent years, and thermal energy management has become a significant issue confronting today's rack, cabinet, frame and enclosure manufacturers, the manufacturers of the electronic equipment, and the users of such equipment.
Typically, multiple racks, frames, cabinets, and the like (sometimes collectively referred to hereinafter as “enclosures”) are housed together in a data center. Because of the overheating problem, and particularly with multiple enclosures being placed in a single room or other enclosed space, thermal management of the data center is very important. A goal of data center thermal management is to maximize the performance, uptime and life expectancy of the active components being housed in the data center. This goal is generally accomplished by managing the cold air delivered to each component such that, the internal temperature of the component does not exceed the manufacturer's maximum allowable operating temperature. Preferably, the cold air delivered to the component is at or below the manufacturer's recommended temperature and in sufficient volume to meet the airflow requirements of the component, which are typically measured in cubic feet per minute (CFM).
A common type of operating environment for enclosures and the equipment mounted therein is known as a “raised floor” system, wherein the enclosures are supported on a heavy-duty mechanical floor that is installed above the actual floor of the room at a given elevation. One significant advantage of this approach is that cables, wires, water pipes, and other utility connections may be routed to and from the enclosures via the space beneath the floor, thereby leaving the top surface of the raised floor clear for locating enclosures and traversal by users. Another significant advantage, however, is that the space beneath the top surface of the raised floor serves as a plenum through which cool air may likewise be distributed to the enclosures. Through open tiles or perforations or ventilations in the tiles comprising the surface of the raised floor, this cool air may be supplied to the enclosures and used to cool the equipment inside.
Unfortunately, the use of perforated floor tiles, typically located directly in front of enclosures to try to cause a maximum amount of cool air to be directed into the enclosures and not merely lost to the ambient room, have been found to be insufficient in cooling the equipment within the enclosures to the desired degree. Thus, a number of techniques and devices have been developed in recent years to more efficiently utilize the capabilities of the Computer Room Air Conditioner (“CRAC”) and to put the available cool air to the most efficient use possible. Among others, these include improved strategies involving perforated panels, such as those described in the commonly-assigned U.S. Provisional Patent Application No. 60/725,511, filed Oct. 10, 2005 and entitled “EFFICIENT USE OF PERFORATED PANELS IN ELECTRONIC EQUIPMENT CABINETS,” and also improved cool air distribution strategies, such as those described in the commonly-assigned U.S. Provisional Patent Application No. 60/743,148, filed Jan. 20, 2006 and entitled “INTERNAL AIR DUCT,” the entirety of each of which is incorporated herein by reference.
The supply of cool air to the raised floor plenum, and the transfer of thermal energy from the electronic equipment, is conventionally handled by the CRAC. Airflow through the plenum and into the enclosures generally relies solely or at least primarily on the air pressure differential as measured between the raised floor plenum and the ambient room. However, active means are often used to push or pull heated air out of the enclosures.
For a particular component, thermal energy is transferred from its housing using forced air convection. More specifically, internal fans draw or push air through the housing from front-to-rear over the heated internal elements within the housing. The air absorbs the thermal energy from the internal elements and carries it away as it exits the housing.
Airflow through a particular component housing is primarily controlled by the internal fan installed by the manufacturer. While it is possible to reduce this throughput by constricting air flow through an enclosure, it is difficult to appreciably increase the airflow through a component housing.
In addition, the rate of transfer of thermal energy from the housing does not change very much for different intake air temperatures. Lowering the intake air temperature reduces the temperature of the processor(s) inside of the component, but the temperature change and the total cooling taking place for the component does not change for a constant airflow. Therefore, any enclosure that does not choke the airflow through the component mounted inside and that prevents recirculation should effectively dissipate most, if not all, of the thermal energy generated by the component.
Recent conventional thinking for the thermal management of data centers involves the use of an approach commonly referred to as the Hot Aisle/Cold Aisle approach. In this strategy, cold air aisles are segregated from hot air aisles by enclosures being positioned between them such that cold air aisles are in front of rows of enclosures and hot air aisles are behind these rows of enclosures. In this approach, the cold air and hot air aisles alternate. Ideally, air enters the enclosure from the cold air aisles and is exhausted from the enclosure into the hot air aisles.
This approach works well in low to medium density data center applications. However, it does not perform well in many medium density applications and can not support high density applications without extreme discipline and additional air flow management devices outside of the enclosures to prevent hot exhaust recirculation into the cold aisle.
Further, Hot Aisle/Cold Aisle data center environments typically do not operate at ideal conditions. Two common problems that affect thermal management in general, and Hot Aisle/Cold Aisle in particular, are recirculation and bypass. Recirculation occurs when hot exhaust air travels back into the component intake air stream. Recirculation can occur for a single component or for an entire enclosure. When this occurs, the exhaust airflow raises intake air temperatures and causes components to run at higher operating temperatures. Bypass occurs when cold source air bypasses the active component and travels directly into the hot exhaust air stream. Similarly to recirculation, bypass may occur for a single component or for a whole enclosure. Because cold source air is bypassing the active component, the air is not serving its intended purpose of transferring thermal energy away from the active component. As such, the bypassing air is essentially wasted, and the active component retains its thermal energy until additional cold source air contacts the active component thereby transferring the thermal energy away from the component. Based on the foregoing, it is readily apparent that bypass wastes energy. In addition, bypass contributes to humidity control problems, and can indirectly contribute to recirculation. Under ideal circumstances, all recirculation and bypass airflow can be eliminated.
Hot Aisle/Cold Aisle is a well-principled thermal management approach, i.e., segregating the cold source air in front of enclosures and hot exhaust air behind them does work. Unfortunately, maintaining the segregation is difficult. In order to maintain proper segregation, the airflow delivered to each enclosure must roughly equal the airflow required by all of the active components in each enclosure. In addition, strict discipline and careful airflow balancing are required to maintain this ideal operating condition in higher density data center environments. While an initial installation may realize these ideal conditions, moves, adds and changes, along with the demands for constantly monitoring and rebalancing, frequently make maintaining this ideal operating condition impractical, if not outright impossible.
For example, one known airflow balancing technique employs variable speed fans that are carefully monitored and controlled using appropriate control methodologies. A drawback to the controlled variable speed fan approach is the unpredictable nature of components, particularly server usage. For example if a server is suddenly heavily burdened by a particular software application, the server heats up, perhaps more quickly than expected, or more than can be handled quickly by a corresponding variable fan. The fan then quickly increases in speed in an attempt to respond to the sudden drastic increase in temperature of the server. The fan may not be able to sufficiently supply cooling air to the suddenly overheated server, and even if it is, such heat balancing procedure is difficult, at best, to manage. It would be better to avoid dependence on such a reactive approach to thermal management.
Cylindrical exhaust ducts have been added to enclosures in an effort to alleviate thermal management issues such as recirculation and bypass. The exhaust ducts generally extend upwardly away from a top surface of the enclosure near the rear of the enclosure and provide a path for hot exhaust air to be expelled. While available exhaust ducts are operative for their intended purpose, an improved design thereof would further aid in alleviating thermal management issues. In addition, it has been found that heated air tends to pool or collect in portions of the interior of enclosures rather than be guided to the exhaust ducts.
As such, a need exists for an improved design of exhaust ducts for component storage enclosures. Further, additional thermal management features are needed in these enclosures. This, and other needs, are addressed by one or more aspects of the present invention.